A conventional general bending device includes an upper table and a lower table located below the upper table, and the tables are opposed to each other. The upper table is provided at its lower side with a punch as an upper die. The lower table is provided at its upper side with a die as a lower die. One of the tables, e.g., the lower table moves in the vertical direction (approaching direction and separating direction) in which the lower table approaches and separates from the upper table by operation of a pair of hydraulic cylinders which are separated from each other in the lateral direction. A moving speed of the lower table is set by a depressing degree of foot pedal or by speed data which is input to a control unit such as an NC device.
The plate-like workpiece is supported on the dies, and the lower table is allowed to move in the vertical direction by the operation of the pair of hydraulic cylinders. With this operation, the punch and the die cooperate, and the workpiece can be bent.
During the bending process in which the upper die comes into contact with the workpiece and most approaches the lower die, if the moving speed of the one movable table in the approaching direction is not appropriate, the following problems come up. That is, when a material of the workpiece is soft or a thickness of the workpiece is thin, if the moving speed of the movable table in the approaching direction during the bending process is too fast, coil breaks are generated in the workpiece, which deteriorates the bending precision. When a length of a bending flange is long, if the moving speed of the movable table during the bending process is too fast, a rebounding speed of the bending flange becomes fast, which is not preferable for operation safety. If the moving speed of the movable table during the bending process is too slow, there is a problem that the operation time becomes too long and the productivity is deteriorated.
The present invention has been achieved in order to solve the problems, and it is a first object of the invention to provide a bending device and a bending method capable of automatically determining a moving speed of a ram in accordance with a material of a workpiece, especially a thickness of the workpiece and a length of a flange so as to eliminate coil breaks of the workpiece.
It is a second object of the invention to provide a bending device and a bending method capable of restraining a rebounding speed of a bending flange from increasing and capable of safely bending a workpiece without posing no danger to an operator by automatically determining the moving speed of a ram in accordance with a flange length of the workpiece.